Various types of picture display devices are conventionally known that display preferred images on picture display elements, such as liquid crystal display panels, and wherein the display images are magnified and observed with an eyepiece.
As an eyepiece used with such picture display devices, Japanese Laid Open Patent Application No. 6-308396 is known. This eyepiece has a curved object plane and aspherical lens element surfaces, thus providing flat and clear images up to the periphery of the image plane while employing only a small number of lens elements.
However, aberrations are favorably corrected in the above-mentioned eyepiece only when the diameter of the exit pupil is about 4 mm (of the embodiments thereof, the brightest one has an FNO of 3.75). The average person""s pupil diameter is considered to be about 3 to 4 mm. No major problems appear even with such a small exit pupil diameter when the eyepiece is used in a motionless state. However, an observer""s pupil and the exit pupil of an eyepiece usually deviate from perfect alignment by as much as 3 to 5 mm if the observation device is used under conditions other than in a motionless state, such as walking, riding in a vehicle, or the like. Therefore, unless various aberrations are favorably corrected out to a large exit pupil diameter, the quality of an observed image will deteriorate under conditions where motions between the eyepiece and the observer occur.
The applicant has already disclosed an eyepiece for a picture display device in Japanese Laid Open Patent Application No. 2000-105344 to solve these problems. This eyepiece is relatively light and compact, yet it has a large exit pupil diameter so that high quality images may be observed under conditions such as walking, riding in a vehicle, or the like.
Although the eyepiece disclosed in Japanese Laid Open Patent Application No. 2000-105344 provides a high quality image under conditions such as walking, riding in a vehicle, or the like, a reduction in the number of lens elements of the eyepiece is desirable since it would make the eyepiece weigh less and be more compact.
Thus, an object of the present invention is to provide an even lighter and more compact eyepiece for a picture display device than in the prior art that is suitable for the viewing of high quality images even while walking, riding in vehicles, or the like.